This invention relates to a digital video tape recorder equipped with separate heads for recording and playing back digital data.
A digital video tape recorder, which converts video signals to digital signals instead of analog signals for recording and playing back the video signals, is being realized. An apparatus on the basis of the recording format indicated in "Design Consideration for the D-2 NTSC Composite Digital VTR", Institute of Television Engineers of Japan Technical Report, Vol. 11, No. 24, pp. 13 to 18 (Oct. 1987) is an example of such a recorder. The recording format of this digital video tape recorder (DVTR) comprises helical tracks (1-channel digital video data and 4-channel digital audio data are recorded) and 3-channel linear tracks as shown in FIG. 3 . Digital data in each field is divided into six tracks for recording. A configuration example of a cylinder and heads to realize such a recording format is indicated in "Mechanical Considerations for Composite Digital VCR" (130th SMPTE Technical Conference, October 15-19, 1988, Preprint No. 130-19). FIG. 4 shows the example. Four recording heads REC1 to REC4 are used for recording digital data for each two channels, and a field is recorded for each 1.5 revolutions of the cylinder. The heads PB1 to PB4 are used for play back. The recording heads and play back heads are separately provided (1) to improve the recording reliability by allowing the play back heads to read signals recorded by the recording heads and by allowing for simultaneous monitoring of the recorded signals and (2) to improve the recording and play back reliability by optimizing the characteristics of the recording heads and play back heads.
Examination shows that, for a combination of a metal tape and ferrite heads, it is required to set the gap length between the recording heads to 0.6 to 1.0 .mu.m and the gap length between the play back heads to 0.2 to 0.4 .mu.m. Therefore, it is difficult due to gap loss to read recorded data perfectly by using the recording heads, and the recording heads are required to be used only for recording data. As a play back head, a movable head is suited for noiseless slow motion play back.
Such a recording head, which is used for play back, can generate a play back output allowing for detection of the output level.